The present invention is directed generally to micro-electromechanical Systems (MEMS) devices and, more particularly, to processes for forming chambers and cavities in a substrate and acoustically interconnecting such structures.
The ability to form moving parts measured in microns has opened up a huge range of applications. Such moving parts typically take the form of a beam or mesh that may form, for example, a variable capacitor, switch, or other component. The recent ability to seal micro-machined meshes has lead to the fabrication of microphones and microspeakers. See, for example, International Publication No. WO/01/20948 A2 published 22 Mar. 2001, entitled MEMS Digital-to-Acoustic Transducer With Error Cancellation, the entirety of which is hereby incorporated by reference.
A sealed mesh can function as a movable plate of a variable capacitor, and therefore can operate as a microphone. For a sealed mesh to operate as a microspeaker, the microspeaker needs to be able to push air to create a soundwave just as its larger counterparts must push air to create soundwaves. Traditional speaker enclosures have a port on the back to allow the speaker to move freely. In the case of a microspeaker, if the chamber beneath the sealed mesh does not have a vent or other opening to ambient, movement of the sealed mesh inward is inhibited by the inability to compress the air in the chamber while movement of the mesh outward is inhibited by formation of a vacuum. Thus it is necessary to form a vent in the chamber if the microspeaker is to create soundwaves.
Currently, such vents are formed by boring through the substrate from the rear. That requires patterning the back side of the substrate followed by an etch through the entirety of the substrate to reach the chamber. Forming of vents by this technique is slow in that several hundred microns of substrate may need to be etched to reach the chamber beneath the sealed mesh and the diameter of the vent is small compared to its depth. Additionally, there are registration problems in that it is necessary to work form the back side of the substrate where there are no landmarks, and hundreds of microns may need to be etched to reach a chamber that may measure in the tens of microns. Thus, the need exists for an easy, repeatable, fast process for forming vents in the chambers of sealed meshes that are to function as speakers.